1. Make your factory restore media.
2. Make a spare ADMIN account that is not tied to an email login. Here's how.
This spare account can help you recover from issues that otherwise has folk factory resetting.
3. It's debatable if you need another Antivirus. Many here use Windows Defender along with safe computing practices. Even if you install another AV that won't save a PC that an owner goes to bad sites or Torrents cracked app.
I just purchased my first laptop. A DELL Inspiron 15" with 7thGen Corei5 and NVIDIA GeForce GTX 1050. What are the first things I should do?